Mobile communication has been one of the most successful innovations in modern history. In recent years, the number of subscribers to mobile communication services has exceeded 5 billion and is growing fast. At the same time, new mobile communication technologies have been developed to satisfy the increasing needs and to provide more and better mobile communication applications and services. Some examples of such systems are cdma2000 1xEV-DO systems developed by Third Generation Partnership Project 2 (3GPP2), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), and Long Term Evolution (LTE) systems developed by 3GPP, and mobile Worldwide Interoperability for Microwave Access (WiMAX) systems developed by the Institute for Electrical and Electronics Engineers (WEE). As more and more people become users of mobile communication systems, and more and more services are provided over these systems, there is an increasing need of a mobile communication system with larger capacity, higher throughput, lower latency, and better reliability.
Conventionally, millimeter waves refer to radio waves with wavelength in the range of 1 mm-10 mm, which corresponds to radio frequency of 30 GHz-300 GHz. These radio waves exhibit unique propagation characteristics. For example, compared with lower frequency radio waves, they suffer higher propagation loss, have poorer ability to penetrate objects, such as buildings, walls, foliage, and are more susceptible to atmosphere absorption, deflection and diffraction due to particles (e.g., rain drops) in the air. Alternatively, due to their smaller wave lengths, more antennas can be packed in a relatively small area, thus enabling high-gain antenna in small form factor. In addition, due to the aforementioned deemed disadvantages, these radio waves have been less utilized than the lower frequency radio waves. This also presents unique opportunities for new businesses to acquire the spectrum in this band at a lower cost. The International Telecommunication Union (ITU) defines frequencies in 3 GHz-30 GHz as SHF (Super High Frequency). Note that some higher frequencies in the SHF band also exhibit similar behavior as radio waves in the EHF (Extra High Frequency) band (i.e., millimeter waves), such as large propagation loss and the possibility of implementing high-gain antennas in small form factors.
Vast amount of spectrum are available in the millimeter wave band. For example, the frequencies around 60 GHz, which are typically referred to as 60 GHz band, are available as unlicensed spectrum in most countries. In the United States, 7 GHz of spectrum around 60 GHz (57 GHz-64 GHz) is allocated for unlicensed use. On Oct. 16, 2003, the Federal Communications Commission (FCC) issued a Report and Order that allocated 12.9 GHz of spectrum for high-density fixed wireless services in the United States (71-76 GHz, 81-86 GHz, and 92-95 GHz excluding the 94.0-94.1 GHz for Federal Government use). The frequency allocation in 71-76 GHz, 81-86 GHz, and 92-95 GHz are collectively referred to as the E-band. It is the largest spectrum allocation ever by FCC—50 times larger than the entire cellular spectrum.
Millimeter wave wireless communication using component electronics have existed for many years. Several companies have developed or are developing millimeter wave communication system that can achieve giga-bits per second (bps) data rate. For example, Asyrmatos Wireless developed a millimeter wave communication system that enables 10 Gbps data transfer over distances of several kilometers. Asyrmatos transceiver is based on photonics, which provides flexibility of operating in a variety of millimeter wave bands such as 140 GHz (F-Band), 94 GHz (W-Band), 70/80 GHz (E-Band), and 35 GHz (Ka-Band). As another example, GigaBeam Corp. developed multigigabit wireless technologies for the 70 GHz and 80 GHz band. However, these technologies are not suitable for commercial mobile communication due to issues such as cost, complexity, power consumption, and form factor. For example, GigaBeam's WiFiber G-1.25 gigabit per second wireless radio requires a two-foot antenna to achieve the antenna gain required for the point-to-point link quality. The component electronics used in these systems, including power amplifiers, low noise amplifiers, mixers, oscillators, synthesizers, waveguides, are too big in size and consume too much power to be applicable in mobile communication.
Recently, many engineering and business efforts have been and are being invested to utilize the millimeter waves for short-range wireless communication. A few companies and industrial consortiums have developed technologies and standards to transmit data at giga-bps rate using the unlicensed 60 GHz band within a few meters (up to 10 meters). Several industrial standards have been developed, e.g., WirelessHD technology, European Computer Manufacturers Association ECMA-387, and IEEE 802.15.3c, with a couple other organizations also actively developing competing short-range 60 GHz giga-bps connectivity technology, such as the Wireless Gigabit Alliance (WGA) and the WEE 802.11 task group ad (TGad). Integrated circuit (IC) based transceivers are also available for some of these technologies. For example, researchers in Berkeley Wireless Research Center (BWRC) and Georgia Electronics Design Center (GEDC) have made significantly progresses in developing low-cost, low-power 60 GHz Radio Frequency Integrated Circuit (RFIC) and antenna solutions. Researchers from BWRC show that 60 GHz power amplifiers can be designed and fabricated in 130 nm bulk “digital” CMOS. A core team of researchers from BWRC co-founded SiBeam Inc. in 2004 and developed CMOS based RFIC and baseband modem for the WirelessHD technology. It is worth mentioning that the common view is that the biggest challenge of short-range 60 GHz connectivity technology is the RFIC. As such, much of the engineering efforts have been invested to develop more power efficient 60 GHz RFICs. Many of the designs and technologies can be transferred to RFIC design for other millimeter wave bands, such as the 70-80-90 GHz band. Although the 60 GHz RFIC today still suffers from low efficiency and high cost, the advancement in millimeter wave RFIC technology points to the direction of higher efficiency and lower cost, which can eventually enable communication over larger distance using millimeter wave RFICs.